Maurice Edu, third from left, stabs home the 90th-minute winner for Rangers against Celtic at Ibrox. Photograph: David Moir/Reuters

Even a Rangers victory could not prevent Walter Smith from taking a clearly preconceived swipe at someone, somewhere at his Old Firm rivals. At the end of a week in which Celtic made their grievances about refereeing decisions public through an unnamed source, controversy was inevitable. It duly arrived when the referee, Dougie McDonald, sent off the visitors' captain, Scott Brown, in the second half, a decision Celtic will cite as almost as crucial to their defeat as Maurice Edu's stoppage-time winner. The club is to appeal against the red card.

Smith, who could be seen leaping around in a manner hardly befitting his 62 years, knew the value of Edu's intervention all right. The Rangers manager's post-match attentions turned towards Celtic, though, and the timing of their alleged leak. "It was a totally unfair circumstance that the referee for this game was placed in this week," Smith said. "It would be nice if somebody who is criticising referees came out of the closet and did it, rather than do so in an anonymous manner."

The cruellest blow yet to Tony Mowbray in his short time as the Celtic manager, and there have been a fair few, should also prove the decisive one. Edu's goal means Mowbray requires a minor miracle to wrestle the Scottish Premier League title from Rangers' grasp. Smith's team are now 10 points ahead of their adversaries and have a game in hand.

"The league is there for Rangers to lose but strange things have happened and will happen in football," said Mowbray, for whom hard-luck tales are proving all too familiar.

Mowbray will be left to contemplate his future if Rangers' lead extends much further. Celtic passed the ball with authority for spells in this game, but failed to create meaningful chances. Amid such a circumstance, their expensive loanee Robbie Keane was a peripheral figure. Keane's arrival, for all it was heralded, has failed to prompt an upturn in Mowbray's fortunes.

Even for this volatile fixture, the atmosphere was noticeably highly charged. A minute's silence in memory of the former Rangers goalkeeper Gerry Neef had been disrupted before a ball was kicked; and kicked it was, battered and smashed around during an utterly frenetic first half.

Matters slowed down marginally after the break, without either team enforcing concerted superiority. Mowbray claimed he did not witness the 66th-minute affair which saw Brown red-carded for a clash with Kyle Lafferty. "A few people in the dressing room have seen it and thought it was a very harsh decision," the manager said.

Rangers were blunt but, once again, found a matchwinner. Edu pounced at close range after Artur Boruc blocked a Kris Boyd shot. Cue bedlam, and the latest sense that Mowbray and Celtic are never destined to be a perfect match.